Which blood type could be given as a transfusion for patient with AB blood when the RH factor is unknown?

A. O+

B. A+

C. AB+

D. AB-

Patient with blood type AB RH + can receive any type of blood, but patient with blood type AB RH - can receive all type of blood which also have RH - factor.

So here if we don't know the RH factor then the safest option is to give this patient AB RH-.

But if we would know that patient have RH + factor then he can receive any blood type no matter what is the RH factor or blood type.

So correct answer is D. AB RH-